The virus spreads by keeping it's code in a file called c:\io.vxd.
The summary information of infected documents is changed to this:
A Study In Espionage Enabled Viruses
Keywords: / Caligula / Opic / Codebreakers /
Comments: The Best Security Is Knowing The Other Guy Hasn't Got Any
The virus hooks the Tools/Macro, Tools/Customize, View/Toolbar and View/statusbar menus. The Tools/Macro menu is greyed out and can't be accessed.
On 31st of each month the virus shows a dialog with this message:
WM97/Caligula (c) Opic [CodeBreakers 1998]
Could map our veins.
The really nasty part of the virus is related to PGP: the virus locates the secret keyring file of PGP (SECRING.SKR) and tries to send it with FTP to a site in the codebreakers.org domain (which is known virus exchange site). To send the key the virus creates temporary file called c:\cdbrk.vxd.
If the attacker can break the passphrase, he can then open PGP encrypted files sent to this user.
This is quite serious as passphrases are the weakest known link today in public key cryptography such as PGP. Also, people very commonly use too weak passphrases. With a copy of the keyring, massive brute-force attacks are possible for any period of time - and the user may not even know if a copy has been made of the keyring.